*Grate the onion on the large holes of a box grater. As you grate it, the onion will release a lot of liquid. That's normal! Add the wet onion pulp to the black bean mixture, leaving excess liquid behind on your work surface.
**These can be made vegan by replacing the egg with a "flax egg" (mix 1 tablespoon ground flaxseed with 2.5 tablespoons warm water and set aside for 5 minutes to thicken). The vegan burgers are cohesive and they cook/grill well, but they're not as firm in the middle as the egg version. I recommend increasing the cooking time slightly on the grill - I do 8 minutes on the first side and 6 minutes on the second side. They're tasty, but my Best Veggie Burger is still my favorite vegan burger.
Keyword black bean burger, plant-based burger, vegan burger, vegetable burger, veggie burger, veggie hamburger